1. Field of the Invention
The invention relates to a pump. In particular, the invention relates to a controllable coolant pump for motor vehicles, which is directly driven by the vehicle's internal combustion engine via a pulley.
2. The Prior Art
Rotary coolant pumps are generally used with water-cooled internal combustion engines. Their bearing shafts are directly driven by the crankshaft of the engine, for example, by tooth belts. With many of these known coolant pumps, the flow chamber is formed in the cylinder crankcase of the internal combustion engine. The bearing casing of the bearing shaft, on whose free end the impeller of the rotary pump is mounted, is detachably connected to the housing of the internal combustion engine. The pulley is arranged on a bearing shaft on one side and the impeller of the rotary pump on the other side. Therefore, the speed or rpm's of the pulley always corresponds with the speed of the impeller of the coolant pump, and is proportional to the given speed of the engine. Shaft seals must be provided on the bearing shaft to seal the flow chamber against the casing of the bearing.
Many kinds of different sealing arrangements for coolant pumps are known in the art. For example, German patents DE 38 19 180, DE 42 03 391, DE 44 09 537 and DE 44 36 879 describe different designs of sealing arrangements. All of the designs described in these patents have sealing units with a sliding ring seal surrounding the bearing shaft for sealing the casing of the bearing against the flow chamber. The sliding ring must rest against a counter ring under the force of at least one pressure spring to ensure that the seal is tight. Therefore, the known sealing units are comprised of a number of different functional assemblies, which are expensive to assemble and/or manufacture, and which are necessarily susceptible to malfunctioning.
Another possibility for reducing problems and for sealing a flow chamber against the driving side has been described, in DD 66 334, U.S. Pat. No. 3,354,833, U.S. Pat. No. 4,674,960 and German Patent DE 41 21 344. These devices employ permanent magnetic rotary front clutches. Two axial multi-pole round magnets magnetized in sectors oppose each other. Since these permanent magnetic rotary front clutches are always synchromesh units, their significant drawback is that the coupling slips when the maximally transmittable moment is exceeded. Such clutches can be re-engaged only after the drive has been stopped. Permanent magnetic rotary front clutches are therefore extremely unsuitable for directly driving a coolant pump of a motor vehicle. For this reason, they have not achieved successful practical application for direct drives.
However, the text of German patent DE 41 21 344 and also the figures of U.S. Pat. No. 3,354,833 show that electric motors, e.g. with electronic controls, are preferably employed for driving rotary front clutches. Such motors then permit gradual start-up as well. Based on the design shown in FIG. 1 of German Patent DE 36 43 565, this device, having a magnetic clutch and direct drive of the water pump impeller, also has the drawback in that the clutch slips when the maximally transmittable torque is exceeded, in addition to having a very low maximally transmittable torque. The design shown in FIG. 2 of that reference does in fact permit transmission of a higher torque. However, due to the type of bearing for the pump impeller, this design leads to elastic deformation of the separation wall and interference with the operational performance.
For this reason, the permanent magnetic central rotary clutch introduced in German Patent DE 41 10 488 was proposed, especially for driving circulating cooling water pumps for motor vehicles. With such designs, the pump impeller is driven by a ring magnet supported within a pot-shaped pump housing. In spite of the fact that the maximally transmittable torque is higher because of the permanent magnets arranged around the circumference, this central rotary clutch is also a synchromesh unit with all the drawbacks described above. In order to prevent an unintentional slipping of clutches of this type for coolant pumps in motor vehicles, these clutches are equipped with additional electric drives as well. Of course, coolant pumps equipped with their own drive can be controlled quite efficiently. However, their space requirements are increased, and they are relatively expensive to manufacture.
A variation of a coolant pump with variable delivery, which is somewhat less expensive, is shown in German Patent DE 43 25 627 and DE 43 35 340. These variations are coolant pumps with a depressive or decreasing delivery system, which are directly driven by the crankshaft. Here, the impeller of the coolant pump is driven not directly by the belt drive, which is depends upon the speed of the engine, but by a known interconnected fluid friction clutch. This clutch is capable of "down"-control at certain excessively high rpms, at which point the depressive delivery behavior improves the cavitation behavior of the coolant circulation by limiting the overall flow volume. According to another embodiment of the invention, this fluid friction clutch can be controlled on the water side depending on the temperature of the coolant. This means that the impeller drive is operated only at a defined idle running speed when the engine is cold, and engages with depressive delivery system depending upon the speed of the engine, only after the coolant reaches a certain temperature.
A significant disadvantage of this controllable coolant engine driven pump having a fluid friction clutch lies in its susceptibility to failure. This potential susceptibility to breakdown of the fluid clutch-controlled coolant pump system is due to the fact that the clutch chamber must be sealed against the flow chamber with a coolant liquid, such as with a silicone oil. If this seal becomes defective during the course of operation, cooling liquid enters the clutch chamber and leads to total failure of the coolant pump, and thus necessarily to total breakdown of the engine.
All other pumps known in the state of art with direct drive by the crankshaft are immediately engaged in the warm-up running phase of the engine. At this time, they start to dissipate the heat generated in the engine, when this heat is urgently needed during the warm-up running phase. As forced cooling is immediately started, the warm-up running phase of the engine is necessarily prolonged. At the same time, this forced cooling, which starts immediately during the warm-up phase leads an to increased fuel consumption in addition to an increase in the emission of exhaust gases. Furthermore, this driving output of the coolant pump, which is not absolutely required for cooling, always results in an increased fuel consumption. This driving output, however, is not equired in this operating condition.